Collins
Spirit, citrus, sugar, soda, over ice in a tall glass.
Defining structure
A Collins is a sour extended with soda water and served long over ice in a tall glass (often called a Collins glass, unsurprisingly). The typical build: two ounces of spirit, one ounce of fresh citrus, three-quarters ounce of simple syrup, shaken briefly, strained into an ice-filled Collins glass, topped with three ounces of club soda. A Collins differs from a highball in that the spirit is acid-tempered with fresh citrus and sugar, not just topped with a long mixer.
History
The Tom Collins is the prototype — named after a running joke in 1870s New York, where patrons would be told 'Tom Collins is out back and speaking ill of you,' sending them on a confused chase through the city's bars. The drink itself emerged through that joke and quickly acquired a recipe. John Collins (the gin-based version) and the Juan Collins (tequila) follow the same template.
Classic examples
Common riffs
Swap the spirit: Tom Collins (gin) becomes Vodka Collins becomes Juan Collins (tequila) becomes Jack Collins (applejack). The French 75 is essentially a Collins topped with Champagne instead of soda — and that substitution transforms the drink's whole character. The Mojito is a Collins with muddled mint and a different ratio of citrus to sugar; some taxonomists call it a highball instead.